Angle transducers are machine components that are widely used for the purposes of guidance and control within industry. The annual consumption of transducers is very large. Such transducers are often used together with gearing in order to increase the resolution of the guided or controlled shaft. For example, with an angle transducer having a resolution of 10,000 increments/revolution and a gear with i=26 times, a resolution for the output shaft of approximately 5 seconds of arc can be achieved.
The disadvantage of this method is that it depends on the precision of the gearing and that it provides poor control of the final precision in the system since this is influenced by play, wear, etc. in the transmission.
Machine-builders strive to place the measurement/angle transducer at the extreme end of the transmission chain, that is, in direct association with the controlled/monitored machine part, in order to avoid such uncontrollable error influences. However, this requires high resolution angle transducers with a resolution of the order of a few seconds of arc or better. A number of products are available on the market with these properties.
The disadvantage of existing angle transducers, however, is that they are very expensive and place high demands on the precision and accuracy in their mounting.
Existing transducers are often of the optical incremental type, which causes them to loose all information if the angular position is changed, for example, following loss of power or switching off of the system. It is thus a major desire that an angle transducer should show absolute values, that is, correct information is to be always available independently of what has occurred during switching off and switching on. This is an advantage in systems for which safety aspects are of major significance. An absolute measurement function allows also design of measuring systems for long-term measurements with small power consumption, since the measuring system can be totally switched off between measurement operations.